1. Field of the Invention
The present invention relates to a catalyst for NOx storage and reduction, a preparation method thereof and a NOx removing system including the catalyst for NOx storage and reduction.
2. Description of the Related Art
NOx is a representative harmful exhaust gas that is emitted from vehicles equipped with the internal combustion engine, and it includes nitric oxide (NO) and nitrogen dioxide (NO2). It is known that NOx causes pulmonary emphysema, bronchitis and the like that are respiratory diseases, and generates ozone that causes smog by photochemical reactions. In recent years, lean-burn engines have been actively developed in order to improve the energy efficiency of the internal combustion engine, thereby lowering CO2 emissions. However, it has been widely recognized that the NOx exhaust from the lean-burn engine is very difficult to remove using the existing three-way catalyst, because of the highly oxidizing environment in the lean-burn engine exhaust due to excess oxygen.
In order to solve health and environmental problems caused by NOx, Europe enacted or proposed regulations such as EURO 3, EURO 4, EURO 5 and current EURO 6. In order to lower the exhaust amount of NOx that is difficult to remove using a known catalyst while the regulation of the vehicle exhaust gas becomes stringent, the vehicle manufacturing industry has been focusing on the development of new engine technologies as well as exhaust after-treatment technologies for cleaner tailpipe emissions.
Among these new technology developments, interests on the development of the NOx storage and reduction catalysts in particular have been growing recently. A NOx removing technology using the NOx storage and reduction catalyst adsorbs NOx under oxygen-rich exhaust gas condition, and reduces it into innocuous gases such as nitrogen and carbon dioxide under hydrocarbon-rich exhaust gas condition.
The catalyst for NOx storage and reduction technology may be normally operated under the lean-burn condition, using the existing exhaust devices without any modifications. Thus, this technology draws special attention from the vehicle manufacturing industry, because it can meet the stringent emission regulations such as EURO 6 without additional infrastructure installation costs.
As a representative storage-reduction catalyst, there may be a catalyst for NOx storage and reduction that includes alumina as a carrier, Ba as a storage material, and a noble metal such as Pt as a NOx reduction catalyst. With the development of the above catalysts, a technology of the NOx storage and reduction has been developed, but in the case of the proposed catalyst for NOx storage and reduction, it has problems in that before and after deterioration and sulfation, there are low storage and reduction activity.
Particularly, development of a catalyst is urgently needed, which does not deteriorate while maintaining its excellent NOx storage and reduction capabilities under the low compression ratio environment and low temperature of around 200° C.
Therefore, inventors of the present invention have extensively investigated a catalyst that has excellent NOx storage and reduction activities before and after deterioration/sulfation, and improved activity, in particular, under the low temperature environment of around 200° C., thereby accomplishing the present invention.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.